This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
Field of the Invention
The present invention relates to the field of data transmission along a tubular body, such as a steel pipe. More specifically, the invention relates to the transmission of data along a pipe within a wellbore or along the surface. The present invention further relates to a hybrid wired-and-wireless transmission system for transmitting data up a drill string during a drilling operation, or along the casing during drilling or production operations.
General Discussion of Technology
It is desirable to transmit data along a pipeline without the need for wires or radio frequency (electromagnetic) communications devices. Examples abound where the installation of wires is either technically difficult or economically impractical. The use of radio transmission may also be impractical or unavailable in cases where radio-activated blasting is occurring, or where the attenuation of radio waves near the tubular body is significant.
Likewise, it is desirable to collect and transmit data along a tubular body in a wellbore, such as during a drilling process. Such data may include temperature, pressure, rate of rock penetration, inclination, azimuth, fluid composition, and local geology. In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. The drill bit is rotated while force is applied through the drill string and against the rock face of the formation being drilled. In order to obtain such information, special downhole assemblies have been developed. These assemblies are generally referred to as Logging While Drilling (LWD) or Measurement While Drilling (MWD) assemblies.
LWD and MWD assemblies allow for more efficient drilling programs. Particularly, bottom hole assemblies having LWD and MWD capabilities are able to store or transmit information about subsurface conditions for review by drilling or production operators at the surface. LWD and MWD techniques generally seek to reduce the need for tripping the drill string and running wireline logs to obtain downhole data.
A variety of technologies have been proposed or developed for downhole communications using LWD or MWD. In one form, MWD and LWD information is simply stored in a processor having memory. The processor is retrieved and the information is downloaded later when the drill string is pulled, such as when a drill bit is changed out or a new bottom hole assembly is installed.
Several real time data telemetry systems have also been proposed. One involves the use of a physical cable such as an electrical conductor or a fiber optic cable that is secured to the tubular body. The cable may be secured to either the inner or outer diameter of the pipe. The cable provides a hard wire connection that allows for real time transmission of data and the immediate evaluation of subsurface conditions. Further, these cables allow for high data transmission rates and the delivery of electrical power directly to downhole sensors.
It can be readily perceived that the placement of a physical cable along a string of drill pipe during drilling is problematic. In this respect, the cable will become quickly tangled and will break if secured along a rotating drill string. This problem is lessened when a downhole mud motor is used that allows for a generally non-rotating drill pipe. However, even in this instance the harsh downhole environment and the considerable force of the pipe as it scrapes across the surrounding borehole can impair the cable.
It has been proposed to place a physical cable along the outside of a casing string during well completion. However, this can be difficult as the placement of wires along a pipe string requires that thousands of feet of cable be carefully unspooled and fed during pipe connection and run-in. Further, the use of hard wires in a well completion requires the installation of a specially-designed well head that includes through-openings for the wires. In addition, if the wire runs outside of a casing string, this creates a potential weak spot in the cement sheath that may contribute to a loss of pressure isolation between subsurface intervals. It is generally not feasible to pass wires through a casing mandrel for subsea applications. In sum, passing cable in the annulus adds significant cost, both for equipment and for rig time, to well completions.
Mud pulse telemetry, or mud pressure pulse transmission, is commonly used during drilling to obtain real time data from sensors at or near the drill bit. Mud pulse telemetry employs variations in pressure in the drilling mud to transmit signals from the bottom hole assembly to the surface. The variations in pressure may be sensed and analyzed by a computer at the surface.
A downside to mud pulse telemetry is that it transmits data to the surface at relatively slow rates, typically at rates of less than 20 bits per second (bps). This rate decreases as the length of the wellbore increases, even down to 10 or even 5 bps. Slow data transmission rates can be costly to the drilling process. For example, the time it takes to downlink instructions and uplink survey data (such as azimuth and inclination), during which the drill string is normally held stationary, can be two to seven minutes. Since many survey stations are typically required, this downlink/uplink time can be very expensive, especially on deepwater rigs where daily operational rates can exceed $2 million. Similarly, the time it takes to downlink instructions and uplink data associated with many other tasks such as setting parameters in a rotary steerable directional drilling tool or obtaining a pressure reading from a pore-pressure-while-drilling tool can be very costly.
The use of acoustic telemetry has also been suggested. Acoustic telemetry employs an acoustic signal generated at or near the bottomhole assembly or bottom of a pipe string. The signal is transmitted through the wellbore pipe, meaning that the pipe becomes the carrier medium for sound waves. Transmitted sound waves are detected and converted to electrical signals for analysis.
U.S. Pat. No. 5,924,499 entitled “Acoustic Data Link and Formation Property Sensor for Downhole MWD System,” teaches the use of acoustic signals for “short hopping” a component along a drill string. Signals are transmitted from the drill bit or from a near-bit sub and across the mud motors. This may be done by sending separate acoustic signals simultaneously—one that is sent through the drill string, a second that is sent through the drilling mud, and optionally, a third that is sent through the formation. These signals are then processed to extract readable signals.
U.S. Pat. No. 6,912,177, entitled “Transmission of Data in Boreholes,” addresses the use of an acoustic transmitter that is as part of a downhole tool. Here, the transmitter is provided adjacent a downhole obstruction such as a shut-in valve along a drill stem so that an electrical signal may be sent across the drill stem. U.S. Pat. No. 6,899,178, entitled “Method and System for Wireless Communications for Downhole Applications,” describes the use of a “wireless tool transceiver” that utilizes acoustic signaling. Here, an acoustic transceiver is in a dedicated tubular body that is integral with a gauge and/or sensor. This is described as part of a well completion.
Another telemetry system that has been suggested involves electromagnetic (EM) telemetry. EM telemetry employs electromagnetic waves, or alternating current magnetic fields, to “jump” across pipe joints. In practice, a specially-milled drill pipe is provided that has a conductor wire machined along an inner diameter. The conductor wire transmits signals to an induction coil at the end of the pipe. The induction coil, in turn, then transmits an EM signal to another induction coil, which sends that signal through the conductor wire in the next pipe. Thus, each threaded connection provides a pair of specially milled pipe ends for EM communication.
A service company, National Oilwell Varco® of Houston, Tex., offers a drill pipe network, referred to as IntelliServ' that uses EM telemetry. The IntelliServ® system employs drill pipe having integral wires that can transmit LWD/MWD data to the surface at speeds of up to 1 Mbps. This creates a communications system from the drill string itself. The IntelliServ® communications system uses an induction coil built into both the threaded box and pin ends of each drill pipe so that data may be transmitted across each connection. Examples of IntelliServe® patents are U.S. Pat. No. 7,277,026 entitled “Downhole Component With Multiple Transmission Elements,” and U.S. Pat. No. 6,670,880 entitled “Downhole Data Transmission System.”
Faster data transmission rates with some level of clarity have been accomplished using EM telemetry; however, it is observed that the induction coils in an EM telemetry system must be precisely located in the box and pin ends of the joints of the drill string to ensure reliable data transfer. For a long (e.g., 20,000 foot) well, there can be more than 600 tool joints. The represents over 600 pipe sections to be threadedly connected. Further, each threaded connection is preferably tested at the drilling platform to ensure proper functioning.
National Oilwell Varco® promotes its IntelliServe® system as providing the oil and gas industry's “only high-speed, high-volume, high-definition, bi-directional broadband data transmission system that enables downhole conditions to be measured, evaluated, monitored and actuated in real time.” However, the IntelliServe® system generally requires the use of booster assemblies along the drill string. These can be three to six foot sub joints having a diameter greater than the drill pipe placed in the drill string. The booster assemblies, referred to sometimes as “signal repeaters,” are located along the drill pipe about every 1,500 feet. The need for repeaters coupled with the need for specially-milled pipe can make the IntelliServe® system a very expensive option.
Recently, the use of radiofrequency signals has been suggested. This is offered in U.S. Pat. No. 8,242,928 entitled “Reliable Downhole Data Transmission System.” This patent suggests the use of electrodes placed in the pin and box ends of pipe joints. The electrodes are tuned to receive RF signals that are transmitted along the pipe joints having a conductor material placed there along, with the conductor material being protected by a special insulative coating.
While high data transmission rates can be accomplished using RF signals in a downhole environment, the transmission range is typically limited to a few meters. This, in turn, requires the use of numerous repeaters.
Accordingly, a need exists for a high speed data transmission system in a wellbore that does not require the machining of induction coils with precise grooves placed into pipe ends or the need for electrodes in the pipe ends. Further, a need exists for such a transmission system that does not require the precise alignment of induction coils or the placement of RF electrodes between pipe joints. In addition, a need exists for a hybrid wired-and-wireless transmission system that does not require special booster assemblies along the drill string but yet provides high speed data transmission.